The present invention relates to a bandpass filter, and particularly, to a TEM dual-mode rectangular-planar dielectric waveguide bandpass filter.
In recent years, marked advances in miniaturization of communication terminals, typically mobile phones, has been achieved thanks to miniaturization of the various components incorporated therein One of the most important components incorporated in a communication terminal is a filter component.
As one type of filter component, TEM dual-mode dielectric waveguide filters are known (A. C. Kundu and I. Awai, xe2x80x9cLow-Profile Dual-Mode BPF Using Square Dielectric Disk Resonator,xe2x80x9d Proceedings of the 1997 Chugoku-region Autumn Joint Conference of 5 Institutes, Hiroshima, Japan, October 1997, page 272). Since the TEM dual-mode dielectric waveguide filter acts as two resonators, i.e., two different modes of the resonator have the same resonant frequency, it can be used as a small and high performance bandpass filter.
However, since the TEM dual-mode dielectric waveguide filter of the above-mentioned type is electrically connected to a printed circuit board by wires, there is the problem that it occupies a relatively wide area. Further, since the electrodes to which the wires are to be connected are disposed on the side surfaces of the dielectric block, for thin types it is difficult to obtain sufficient external circuit coupling and/or it is difficult to perform a wire bonding.
Moreover, since the TEM dual-mode dielectric waveguide filter of the above-mentioned type has the removed portion on the metal plate which is floating for controlling the coupling, there is the further problem that the radiation loss increases with increasing the area of the removed portion so as to enhance the coupling.
It is therefore an object of the present invention to provide an improved TEM dual-mode dielectric waveguide bandpass filter.
Another object of the present invention is to provide a very thin TEM dual-mode dielectric waveguide bandpass filter.
A further object of the present invention is to provide a TEM dual-mode dielectric waveguide bandpass filter which requires a small area for mounting.
A still further object of the present invention is to provide a TEM dual-mode dielectric waveguide bandpass filter having sufficient external circuit coupling. A still further object of the present invention is to provide a TEM dual-mode dielectric waveguide bandpass filter in which the radiation loss is decreased.
The above and other objects of the present invention can be accomplished by a bandpass filter of dual modes comprising a dielectric block having a top surface, a bottom surface and first to fourth side surfaces, a first metal plate to be in a floating state substantially entirely formed on the top surface of the dielectric block, a second metal plate to be grounded formed on the bottom surface of the dielectric block, and means for providing a coupling between the dual modes.
According to the present invention, because the top surface of the dielectric block is substantially entirely covered with the first metal plate to be in a floating state, the radiation loss can be reduced.
In a preferred aspect of the present invention, the providing means is achieved by a removed portion exposing a part of the bottom surface of the dielectric block.
In another preferred aspect of the present invention, the providing means is achieved by a coupling control stub formed on the bottom surface of the dielectric block and physically connected to the second metal plate.
In still another preferred aspect of the present invention, the providing means is achieved by a third removed portion exposing still another part of the bottom surface of the dielectric block.
In a further preferred aspect of the present invention, the bandpass filter further comprises a first exciting electrode and a second exciting electrode formed on the bottom surface of the dielectric block.
According to this preferred aspect of the present invention, because the exciting electrodes are disposed on the bottom surface of the dielectric block, the thickness there of the dielectric block and the area for mounting can be reduced. Moreover, because sufficient external circuit coupling can be obtained, a very thin shape and broadband operation can be achieved simultaneously.
In another preferred aspect of the present invention, the bandpass filter further comprises a first exciting electrode formed on the first side surface of the dielectric block and a second exciting electrode formed on the second side surface adjacent to the first side surface of the dielectric block
The above and other objects of the present invention can be also accomplished by a bandpass filter of dual mode comprising a dielectric block having a top surface, a bottom surface and first to fourth side surfaces, a first metal plate formed on the top surface of the dielectric block, a second metal plate formed on the bottom surface of the dielectric block, first and second exciting electrodes formed on the bottom surface of the dielectric block, and means for providing a coupling between the dual modes.
According to the present invention, because the exciting electrodes are disposed on the bottom surface of the dielectric block, the thickness there of the dielectric block and the area for mounting can be reduced. Moreover, because sufficient external circuit coupling can be obtained, a very thin shape and broadband operation can be achieved simultaneously.
In a preferred aspect of the present invention, the providing means is achieved by a removed portion exposing a part of the bottom surface of the dielectric block.
In another preferred aspect of the present invention, the providing means is achieved by a coupling control stub formed on the bottom surface of the dielectric block and physically connected to the second metal plate.
In still another preferred aspect of the present invention, the providing means is achieved by a third removed portion exposing still another part of the bottom surface of the dielectric block.
The above and other objects and features of the present invention will become apparent from the following description made with reference to the accompanying drawings.